Abstract: In order to reflect the influence of small-strain nonlinear stiffness evolution and stress-path-dependent effect of soft soil on foundation pit deformation, a three-dimensional finite element numerical model for soft soil deep foundation pit deformation considering the cumulative degradation effect of shear modulus with shear strain is established, which is based on the elastic-plastic anisotropic boundary surface model considering intergranular strain (IGS). Based on the deep foundation pit project of an underground sewage treatment plant in Shanghai, three-dimensional finite element numerical simulations of the whole process of foundation pit construction are carried out, and the results are compared with the field deformation monitoring results. The results show that the numerical simulation based on the IGS constitutive model considering shear modulus degradation effect can reasonably reproduce the evolution law of horizontal displacement and surface settlement of diaphragm wall, and can reflect the influence of small-strain stiffness evolution on deformation concentration. The simulation results can provide a useful reference for the design optimization and construction deformation control of deep foundation pits in soft soil.